1. Field of the Invention
The present invention relates to a compressor which is preferably applicable to an electric compressor for a refrigeration cycle.
2. Description of Prior Art
According to an invention disclosed in JP-A-7-71388, for example, lubricating oil flowed into a motor housing with refrigerant from a compressing mechanism is led to the compressing mechanism (sliding portion of a compressor) via a lubricating oil passage formed on a middle housing.
Generally, the lubricating oil passage is formed by drilling a hole in a housing. Thus, if the passage length is long compared to the passage bore, a drill may be easily broken, and machining may be difficult. On the other hand, if the passage bore is too large, highly pressurized refrigerant returns to low pressure side (suction side of the compressing mechanism) together with the lubricating oil, thereby reducing the efficiency of the compressor.
Then, according to the above prior art, after forming a lubricating oil passage having a comparatively large bore, a pin-shaped contraction means is inserted and installed in the lubricating oil passage to reduce cross sectional area of the lubricating oil passage, and the highly pressurized refrigerant is prevented from returning to the low pressure side (suction side of the compressing mechanism) with the lubricating oil.
According to the above prior art, however, it is necessary to install the contraction means (contraction pin) in the lubricating oil passage. Accordingly, the prior art has a disadvantage as to reducing the manufacturing cost because it requires the contraction means and certain manufacturing processes for the contraction means.
Furthermore, it is necessary to machine a counter boring at a place of the lubricating oil passage in which the contraction pin is inserted. Accordingly, the passage structure is complicated, and it may be difficult to reduce the machining processes (time) for the counter boring.